1. Field of the Invention
The present invention relates to a liquid crystal display device and a manufacturing method thereof.
2. Description of the Related Art
An example of a basic constitution of a liquid crystal display device which uses thin film transistors (also referred to as xe2x80x9cTFTsxe2x80x9d in this specification) as driving elements is constituted as follows. TFTs, scanning lines or signal lines are formed on a first transparent substrate, color filters are formed on a second transparent substrate, and liquid crystal is inserted into a gap between the first and second transparent substrates while arranging a TFT forming surface or a color filter forming surface at the inside of the respective substrates. The TFTs on the first substrate are arranged on respective pixel regions. Further, with respect to color filters on the second substrate, color regions consisting of red (R), green (G), blue (B) are arranged in a stripe shape and a black matrix constitution made of metal is adopted as partitions for color filters (also referred to as xe2x80x9cCFsxe2x80x9d in this specification) of respective colors CF. The brightness, that is, the numerical aperture of the liquid crystal display device having such a constitution is largely reduced when the positioning accuracy of the first and second substrates is poor and this adverse influence is worse than the positioning accuracy among the TFTS, the scanning lines and the signal lines on the first substrate. Accordingly, there has been publicly proposed a technique which is generally called xe2x80x9ca color-filter on TFTsxe2x80x9d. This technique is characterized by simultaneously forming color filters and a black matrix which have been formed on the second substrate conventionally along with the formation of the TFTs, the scanning lines, the signal lines or the like on the first substrate.
On the other hand, as a system which broadens a viewing angle of the liquid crystal display device, there have been proposed an IPS (In-Plane-Switching) type and a FSS (Fringe-Field-Switching) type. In the IPS type, by rotating liquid crystal molecules substantially horizontally with respect to substrates, pixel electrodes and common electrodes for driving liquid crystal are simultaneously formed on the first substrate and an electric field is generated substantially horizontally with respect to the substrates by applying a voltage between two electrodes. In the FSS type, either one of the pixel electrodes and the common electrodes are formed in a planar shape without forming them in a comb-like shape and comb-like electrodes are formed on the electrodes by way of an insulation film. The FSS type is disclosed in Japanese Laid-open Patent Publication 202356/1999.
Further, a method which realizes a color filter/on/TFT using the IPS type is disclosed in Japanese Laid-open Patent Publication 111957/2000.
However, in Japanese Laid-open Patent Publication 111957/2000, pixel electrodes which apply an electric field to a liquid crystal layer are arranged on an upper portion of a color filter layer via through holes formed in the color filter layer. The through hole is formed for each pixel. However, inventors of the present invention have found a serious problem with respect to the mass-productiveness or the yield factor that the clogging of these through holes gives rise to the large reduction of the yield factor according to a result of an experiment. Further, in the IPS display type, the dielectric constant is low and due to the voltage dividing effect brought about by the color filter layer whose thickness is greater than a film thickness of an inorganic insulation film on the TFT. Accordingly, when the through holes are not formed as described in Japanese Laid-open Patent Publication 111957/2000, it is impossible to apply a sufficient voltage to the liquid crystal layer so that there arises a problem that the transmittivity is lowered.
Further, Japanese Laid-open Patent Publication 202356/1999 discloses a constitution in which, to rotate liquid crystal molecules horizontally with respect to the first substrate, common electrodes which are not formed in a comb shape are formed on the first substrate and pixel electrodes formed in a comb shape are formed on the common electrodes by way of an insulation film. However, color filters are not formed on the first substrate and there is no technical disclosure including problems related with the color- filter-on TFTs. On the other hand, Japanese Laid-open Patent Publication 111957/2000 discloses one system of the color-filter-on TFTs which use the IPS type. The system, in a cross-sectional structure thereof, while adopting a constitution in which a transparent insulation is provided between pixel electrodes and common electrodes as a basic constitution, forms resin-made color layers which constitute color filter layers into given thickness of red (R), green (G) and blue (B) depending on the color arrangement of respective pixel and are patterned. Accordingly, after forming the usual TFTs, the color filter CF layers R, G, B are formed through the photo-patterning three times. Then, comb electrodes which constitute either one of the pixel electrodes and the common electrodes are formed and then, a transparent insulation film is formed. Further, comb electrodes which constitute the other one of the pixel electrodes and the common electrodes are formed. In this manner, there has been a problem that the steps are extremely long. Further, such lengthy steps increases chances of positioning of exposure on the first substrate on which the TFTs are formed. Accordingly, when the manufacturing steps are performed while ensuring the margin for positioning, there arises a problem that the original purpose of the color-filter-on TFTs to provide a bright liquid crystal display device by increasing the numerical aperture and the transmittivity is not achieved.
Accordingly, it is an object of the present invention to solve the above-mentioned problems and it is an first object of the present invention to provide a TFT liquid crystal display device which arranges pixel electrodes and common electrodes which drive a liquid crystal layer on a first glass substrate and also incorporates color filter layers therein without forming through holes for respective pixels.
Further, it is a second object of the present invention to provide a liquid crystal display device which forms not only TFTs but also CFs on a first substrate at the time of forming the liquid crystal display device having a broad viewing angle by horizontally rotating liquid crystal molecules with respect to substrates using a simplified manufacturing method and a method for manufacturing such a liquid crystal display device.
Further, it is a third object of the present invention to provide a liquid crystal display device which exhibits the high numerical aperture and the high transmittivity and a method for manufacturing the liquid crystal display device.
Further objects of the present invention will be apparent from the description of this specification.
To briefly explain typical means for solving the above-mentioned problems, they are as follows.
(Means 1)
In a liquid crystal display device which includes first and second transparent substrates and a liquid crystal layer which is sandwiched between the first and second substrates, wherein the first substrate includes a plurality of video signal lines, a plurality of scanning signal lines and a plurality of pixel regions which are formed as regions surrounded by the video signal lines and the scanning signal lines, each pixel region includes at least one active element and one pixel electrode, and color filter layers are formed between the pixel electrodes and the liquid crystal layer, a boundary between color filters of pixels which are arranged close to each other in the extending direction of the scanning signal lines is positioned on the video signal line and, at the same time, a light shielding layer is formed between the color filters and the liquid crystal layer such that the light shielding layer is superposed on the boundary portion and the video signal line.
Due to such a constitution, the manufacturing steps can be shortened. Further, by forming the boundary of the color filter on the video signal line and by forming the light shielding layer which shields light made incident on the boundary region, a liquid crystal display device which can reduce the margin for positioning and can enhance the numerical aperture can be realized.
(Means 2)
In a liquid crystal display device which includes first and second transparent substrates and a liquid crystal layer which is sandwiched between the first and second substrates, wherein the first substrate includes a plurality of video signal lines, a plurality of scanning signal lines and a plurality of pixel regions which are formed as regions surrounded by the video signal lines and the scanning signal lines, each pixel region includes at least one active element, one pixel electrode and one common electrode, and color filter layers are formed between the pixel electrodes and the liquid crystal layer, the common electrodes are formed as layers above the color filters and the pixel electrodes are formed as layers below the color filters, and the color filters are formed to be superposed on at least the entire surfaces of the pixel electrodes in the pixel regions.
Due to such a constitution, it becomes possible to provide a TFT liquid crystal display device which arranges the pixel electrodes and the common electrodes which drive the liquid crystal layer on the first glass substrate and also incorporates the color filter layers without forming a through hole for each pixel.
(Means 3)
In a liquid crystal display device which includes first and second transparent substrates and a liquid crystal layer which is sandwiched between the first and second substrates, wherein the first substrate includes a plurality of video signal lines, a plurality of scanning signal lines and a plurality of pixel regions which are formed as regions surrounded by the video signal lines and the scanning signal lines, each pixel region includes at least one active element, one pixel electrode and one common electrode, and color filter layers are formed between the pixel electrodes and the liquid crystal layer, the common electrodes and the pixel electrodes are formed as layers below the color filters and the color filters are formed to be superposed on at least the entire surfaces of the pixel electrodes and of the common electrodes in the pixel regions.
Also according to such means, in the same manner as means 2, it becomes possible to provide a TFT liquid crystal display device which arranges the pixel electrodes and the common electrodes which drive the liquid crystal layer on the first glass substrate and also incorporates the color filter layers thereon without forming a through hole for each pixel.
(Means 4)
In a liquid crystal display device which includes first and second transparent substrates and a liquid crystal layer which is sandwiched between the first and second substrates, wherein common electrodes are provided to at least one of the first and second substrates, the first substrate includes a plurality of video signal lines, a plurality of scanning signal lines and a plurality of pixel regions which are formed as regions surrounded by the video signal lines and the scanning signal lines, each pixel region includes at least one active element and one pixel electrode, and color filter layers are formed between the pixel electrodes and the liquid crystal layer, the color filters are formed between the pixel electrodes and the common electrodes, and a driving electrode for the liquid crystal layer is generated along a path which passes both of the liquid crystal layer and the color filter between the pixel electrode and the common electrode.
Due to such an arrangement, the driving electric field can be applied to the liquid crystal layer which is sandwiched between the color filter layers and the second substrate without forming a through hole in the color filter layer of each pixel. Since the through holes are not formed in the color filter layers, the positioning accuracy between respective layers can be enhanced so that the numerical aperture can be enhanced and the bright TFT liquid crystal display device can be realized.
To explain examples of the means of the present invention, they are as follows.
To apply a larger electric field to the liquid crystal layer, the pixels or the common electrodes which are formed in the color filter layers are formed in a planar comb shape, the common electrodes or the pixel electrodes which are arranged below the color filters are formed in a rectangular shape, ends portions of at least the above-mentioned comb electrodes are superposed on rectangular electrodes which are disposed below the comb electrodes, and the intensity of electric field between the common electrodes and the pixel electrodes is determined by the film thickness of an insulation film which is sandwiched between the above-mentioned common electrode and pixel electrode. Further, the pixel electrodes or the common electrodes are formed in a planar comb shape, the common electrodes or pixel electrodes which are arranged below the color filters are formed in a rectangular shape, ends portions of at least the above-mentioned comb electrodes are superposed on rectangular electrodes which are disposed below the comb electrodes, and the intensity of electric field between the common electrodes and the pixel electrodes is determined by the film thickness of an insulation film which is sandwiched between the above-mentioned common electrode and pixel electrode, and the color filter layers are formed above the comb electrodes.
In a liquid crystal display device which can achieve other object of the present invention, the color filter layers are superposed on at least two or more layers to give a function of light shielding films for TFTs to the color filter layers thus simplifying the manufacturing steps.
In a liquid crystal display device which can achieve other object of the present invention, the color filter layers are separated along the neighboring drain lines such that the color filter layers are not superposed with each other, or the color filter layers are separated for respective pixels. Accordingly, the color filter having high transmittivity can be used and, at the same time, the color filter layers per se can be used as electrodes whereby it becomes possible to provide a bright TFT liquid crystal display device which can lower a driving voltage.
Further, to explain means to provide a bright TFT liquid crystal display device, they are as follows.
In a liquid crystal display device which includes first and second transparent substrates and a liquid crystal layer which is sandwiched between the first and second substrates, wherein the first substrate includes a plurality of video signal lines, a plurality of scanning signal lines and pixel regions which are formed as regions surrounded by the neighboring respective lines consisting of the video signal lines and the scanning signal lines, and each pixel region includes at least one active element and one pixel electrode, light shielding layers and the common electrodes are formed on the video signal lines by lamination by way of an insulation film, the light shielding layers are made of metal, and the common electrodes are made of a transparent conductive body.
Portions of the common electrodes which may preferably be disposed above the video signal lines have a width wider than that of the light shielding layers.
The common electrodes may preferably be laminated to upper layers of the light shielding layers.
The common electrodes may preferably be laminated to lower layers of the light shielding layers.
The common electrodes may preferably be superposed on the light shielding layers above the video signal lines and the common electrodes are not superposed on the light shielding layers at the display regions between the video signal lines.
The pixel electrodes may preferably be comb-shaped.
The pixel electrodes may preferably be comb-shaped and formed below the insulation films.
The insulation films may preferably be formed of color filters and are positioned along the video signal lines so as to define boundary portions.
The insulation films may preferably be formed of organic films.
The light shielding layers may preferably be also formed on the scanning signal lines.
Further means and effects of the present invention will become apparent from this specification including claims.